LT3592IMSE datasheet(7/24 Pages) LINEAR

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LT3592

3592fc

PIN FUNCTIONS

RT(Pin1):Programsthefrequencyoftheinternaloscillator.

Connect a resistor from RT to ground. Refer to Table 1 or

the Typical Performance Characteristics for resistor values

that result in desired oscillator frequencies.

BRIGHT (Pin 2): Used to program a 10:1 dimming ratio

for the LED current. Drive this pin above 1.4V to command

maximum intensity or below 0.3V to command minimum

intensity. This pin can be PWMed at 150Hz for brightness

control between the 1x and 10x current levels.

SHDN (Pin 3): Used to shutdown the switching regulator

and the internal bias circuits. This pin can be PWMed at

150Hz for brightness control.

VIN (Pin 4): Supplies current to the LT3592’s internal cir-

cuitry and to the internal power switches. Must be locally

bypassed. For automotive applications, a pi network with a

cap from VIN to GND, a series inductor connected between

VIN and the power source, and another cap from the far

end of the inductor to GND is recommended.

DA (Pin 5): Allows the external catch diode current to be

sensed to prevent current runaway, such as when VIN is

high and the duty cycle is very low. Connect this pin to

the anode of the external catch Schottky diode.

SW (Pin 6): The SW pin is the output of the internal power

switch. Connect this pin to the inductor and the cathode

of the switching diode.

BOOST (Pin 7): Provides a drive voltage, higher than the

input voltage to the internal bipolar NPN power switch.

BOOST will normally be tied to the SW pin through a 0.1μF

capacitor. An internal Schottky is provided for the boost

function and an external diode is not needed. An external

Schottky diode should be connected between BOOST and

CAP for single LED applications or whenever a higher

BOOST voltage is desired.

CAP (Pin 8): Output of the step-down converter and also

an input to the LED current sense ampliﬁer. Connect the

ﬁlter capacitor, inductor, and the top of the external LED

current sense resistor to this pin.

OUT (Pin 9): Drives the LED or LEDs and is the other

input to the LED current sense ampliﬁer. Connect this pin

to the anode of the top LED in the string, the bottom of

the external LED current sense resistor, and the top of the

VFB resistor divider.

VFB (Pin 10): The feedback node for the output voltage

control loop. Tie this node to a resistor divider between OUT

and GND to set the maximum output voltage of the step-

down converter according to the following formula:

OUT = 1.21•

R1+ R2

where R1 connects between OUT and VFB and R2 connects

between VFB and GND.

Exposed Pad (Pin 11): Ground. The underside exposed

pad metal of the package provides both electrical contact

to ground and good thermal contact to the printed circuit

board. The device must be soldered to the circuit board

for proper operation.

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